[PowerPC] Fix to guard fetch and cas 64-bit builtin versions

The builtins: `__compare_and_swaplp`, `__fetch_and_addlp`,
` __fetch_and_andlp`, `__fetch_and_orlp`, `__fetch_and_swaplp` are
64 bit only. This patch ensures the compiler produces an error in 32 bit mode.

Reviewed By: #powerpc, nemanjai

Differential Revision: https://reviews.llvm.org/D110824